Questions: Do behavioural, morphological, and life-history responses to predators differ among offspring of laboratory and newly captured snails from the same field site? The risk allocation hypothesis states that prey should balance predator avoidance and feeding time according to the degree of predation risk. Are there patterns in behavioural, morphological, and fitness traits that provide insight into predictions of this hypothesis?

Organism: We used offspring from two parentage lines of the freshwater gastropod, Physa pomilia, obtained from the exact same stream location but either (1) maintained in the laboratory for 3–4 generations or (2) newly field captured.

Methods: We employed a caged-snail design in which offspring obtained from the laboratory culture and the newly field-captured snails were both exposed to a crayfish predator cue plus alarm cue for 40 days. We assessed behavioural, morphological, and fitness-related traits and conducted a short-term predator avoidance assay at the end of the 40-day experiment.

Results: Over 40 days, offspring of newly caught and laboratory snails displayed similar proportions of predator avoidance behaviour on average. However, offspring of newly caught snails decreased their predator avoidance behaviour over time, as predicted by the risk allocation hypothesis, while offspring of laboratory snails did not. These differences were confirmed with a short-term behavioural assay. Offspring of newly caught snails also developed thicker shells with longer and narrower apertures than the offspring of laboratory snails, making them more predator resistant, which may have explained differences in behavioural responses. Predator cues strongly reduced total egg mass production. Egg mass production was greater in the offspring of laboratory snails under predator-free conditions but greater in the offspring of newly caught snails when exposed to predator cues. The results highlight the importance of population history in studies of phenotypic plasticity.

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